Potential combinations of endocannabinoid/endocannabinoid-like compounds and antibiotics against methicillin-resistant Staphylococcus aureus
Mark Feldman, Reem Smoum, Raphael Mechoulam, Doron Steinberg
PLoS One, April 15, 2020, 1-13.
Doi : 10.1371/journal.pone.0231583
Infections caused by antibiotic-resistant strains of Staphylococcus aureus have reached epidemic proportions globally. Our previous study showed antimicrobial effects of anandamide (AEA) and arachidonoyl serine (AraS) against methicillin (MET)-resistant S. aureus (MRSA) strains, proposing the therapeutic potential of these endocannabinoid/endocannabinoid-like (EC/EC-like) agents for the treatment of MRSA. Here, we investigated the potential synergism of combinations of AEA and AraS with different types of antibiotics against MRSA grown under planktonic growth or biofilm formation. The most effective combinations under planktonic conditions were mixtures of AEA and ampicillin (AMP), and of AraS and gentamicin (GEN). The combination with the highest synergy in the biofilm formation against all tested bacterial strains was AEA and MET. Moreover, the combination of AraS and MET synergistically caused default of biofilm formation. Slime production of MRSA was also dramatically impaired by AEA or AraS combined with MET. Our data suggest the novel potential activity of combinations of EC/EC-like agents and antibiotics in the prevention of MRSA biofilm formation.
The ability of bacterial pathogens to adapt and to overcome the challenges of antibiotics is a life-threatening problem that has emerged in the last few decades. Today, the increase in multidrug- resistant strains is a serious concern.
Despite the fact that Staphylococcus aureus are natural inhabitants of the human microbiota, severe staphylococcal infections can occur on epithelial surfaces , as well as in the bloodstream [2, 3]. S. aureus are very well adapted in the human body and extremely resistant to newly developed antibiotics with new targets of action. It has been postulated that these bacteria can develop resistance to any antibiotic . Indeed, diseases associated with antibioticresistant strains of S. aureus, including methicillin (MET)-resistant S. aureus (MRSA), have spread globally  and are rapidly increasing in both healthcare and community settings [6– 8]. In addition, the highly virulent community-associated MRSA strain causes tissue-destroying infections, such as necrotizing fasciitis and fulminant necrotizing pneumonia .
S. aureus can form biofilms on biotic and abiotic surfaces during infection. Very often, these biofilms are highly resistant to antimicrobials and are difficult to eradicate by host immune factors, since they act to protect bacteria from the effects of both antibiotics and the host immune system. Staphylococci in a biofilm environment have been shown to acquire heritable antibiotic resistance through spontaneous mutation , as well as plasmid-borne antibiotic resistance .
The EC system (ECS) is a biological system composed of EC, which are endogenous arachidonate- based lipids that bind to cannabinoid receptors, CB1 and CB2 that are expressed throughout both the central and peripheral nervous systems and peripheral organs. Enzymes in ECS are involved in synthesis and degradation of EC. CB1 and CB2 are activated by various substances such as EC or phytocannabinoids that occur naturally in the cannabis plant or synthetic cannabinoids . The ECS is involved in the regulation of several physiological processes, including sleep and the immune response. Anandamide (AEA) is one of the main endogenous ligands of the cannabinoid receptors, recruited during tissue injury to provide a first response to nociceptive signals [13, 14]. Arachidonoyl serine (AraS), an EC-like lipid initially isolated from bovine brain, has been found to weakly bind to CB1 and CB2 receptors . AraS demonstrates neuroprotection related to indirect signaling via the CB2 receptor . Both agents contribute to the maintenance of vascular integrity and angiogenesis [17, 18]. Moreover, AEA has been shown to diminish the inflammatory response in periodontitis . A few studies have reported the antimicrobial effects of cannabis extracts against different pathogens , and anti-MRSA activity of exogenous cannabinoids . In addition, we have shown that single AEA and AraS effectively alter the pathogenicity of different MRSA strains .
In the present study, we investigated the potential synergistic effects of combining EC and EC-like compounds AEA and AraS with different antibiotics against MRSA growing under planktonic growth or biofilm formation.